1. Field of the Invention
The present invention relates generally to a device for visually indicating a current location of a vehicle. More particularly, the invention relates to an improved apparatus for determining and visually indicating a current location of an automotive vehicle to the driver thereof, wherein a stable and quick-start locating operation is attained from the combination of an earth magnetism sensor and a rate type gyroscope by the selection of one of the two which suits the particular situation at hand.
2. Description of Relevant Art
A known apparatus has been developed for the determination and visual indication of a current location of an automotive vehicle to the driver thereof which comprises a travel distance counter section adapted to determine the current mileage or travel distance of an automotive vehicle in terms of, for example, its travel speed, and a bearing detector section adapted to detect the current orientation and extent of azimuthal deviation of the vehicle in accordance with its travel direction per a given distance from its starting point. The current location of the vehicle along its travel route is obtained arithmetically from the thus-obtained detection data, the result of which calculation is visually indicated on a display for the driver of the vehicle by way of spot information varying from time to time upon a suitable road map shown in the display indicating the travel route along which the vehicle is currently travelling.
In the aforesaid known apparatus for visually indicating a current location of an automotive vehicle, an earth magnetism sensor is employed as a bearing detection means, which is designed to sense the earth magnetism so that it may detect a current relative relationship such as, for example, a current angular relationship between the orientation of a current horizontal component of the earth magnetism and a current travel direction of the vehicle.
In such a bearing detecting apparatus which employs an earth magnetism sensor, because such apparatus can consistently present the absolute orientation of the vehicle with respect to a current location thereof, unlike one which employs a rate type gyroscope in which it is very possible that errors will be accumulated in the bearing detection as developed from possible drifts of the gyroscope during vehicle operation to such an extent that information obtained from the thus-accumulated errors present an erroneous locating indication of the vehicle on the display screen, it is possible for the bearing detecting apparatus of the earth magnetism sensor type to provide relatively stable operation on the average for a long distance. In contrast, however, from a short-term standpoint, the earth magnetism sensor type bearing detecting apparatus is inconveniently substantially susceptible to disturbances from external structures such as a railroad crossing or an iron bridge which the vehicle may pass by, or when a large-sized truck travels near to the vehicle, so that the display presents undesired incorrect information on a current location to the driver of the vehicle which deviates from a predetermined course of travel due to the thus-far accumulated errors in the location detecting.
When the vehicle provided with the aforesaid type bearing detecting apparatus is subject to the foregoing conditions, it is very difficult or even impossible for the driver thereof to determine whether the displayed information on the screen is incorrect or if the vehicle is actually travelling in a different or incorrect way, thus resulting in substantial ambiguity.
The present invention effectively overcomes the foregoing inconveniences and difficulties experienced with the conventional location detecting apparatus for use in an automotive vehicle.